Thromboembolic disease, i.e. blockage of a blood vessel by a blood clot, affects many adults and can be a cause of death. Most spontaneously developing vascular occlusions are due to the formation of intravascular blood clots known as thrombi, which finally block the artery at the point of their formation. Such occlusions are known as thrombotic occlusions. Alternatively, small fragments of a clot (emboli) may detach from the body of the clot and travel through the circulatory system to lodge in distant organs. These emboli are then trapped and may cause serious complications interfering with normal circulation. Such occlusions caused by a clot that forms elsewhere in the body and travels through the bloodstream are known as embolic occlusions. Cerebral infarction (stroke), myocardial infarction (heart attack) and renal and pulmonary infarcts are well known consequences of thromboembolic phenomena. Obstruction of the blood vessel may also cause a secondary rupture or leakage in arterial walls and subsequent bleeding (haemorrhage). Primary rupture of a blood vessel occurs without thrombotic or embolic occlusion e.g. at the site of aneurysm (weakened area in the wall of artery). Examples of primary cerebral bleeding include intracranial haemorrhage and subarachnoidal haemorrhage.
Fibrin is a major protein component of a clot which forms a relatively insoluble network. Clots are formed when soluble fibrinogen, which is present in high concentrations in blood, is converted to insoluble fibrin by the action of thrombin. Proteolytic, particularly fibrinolytic enzymes, have been used to dissolve vascular occlusions, since disruption of the fibrin matrix results in dissolution of the clot.
Also mammalian blood contains a fibrinolytic system, called plasminogen system, which plays role in thrombolysis. The fibrinolytic system contains plasminogen, which by the action of plasminogen activators (PA) is converted to the active enzyme plasmin, which in turn digests fibrin to soluble degradation products. Two physiological plasminogen activators, called tissue-type (t-PA) and urokinase-type (u-PA), have been identified.
Inhibition of plasminogen activation is achieved by plasminogen activator inhibitor-1 (PAI-1), which forms a stable inactive complex with t-PA. The majority of clot-responsive PAI-1 accumulates within the thrombus rendering it initially resistant to fibrinolysis. An elevated PAI-1 level constitutes an important thrombotic risk factor e.g. for myocardial infarction or deep venous thrombosis because of an overall increased antifibrinolytic potential.
PAI-1 becomes functionally stabilized only in complex with vitronectin (VN), an abundant plasma glycoprotein. Moreover, VN plays a critical role in PAI-1 binding to fibrin. Similar to PAI-1, high molecular weight kininogen (HK) also binds to VN and compete with PAI-1 for proximal binding sites of VN. Thus, kininogen (HK) can inhibit the formation of or dissociate PAI-1-VN complex and thereby contribute to a diminution of PAI-activity. Indeed, studies have shown kininogen (HK) to be antithrombotic rather than prothrombotic, and patients deficient of kininogen (HK) are at increased risk of thrombosis. See Chavakis, T. et al., “A Novel Antithrombotic Role for High Molecular Weight Kininogen as Inhibitor of Plasminogen Activator Inhibitor-1 Function”, Journal of Biological Chemistry, 277, 36, 32677-32682 (2002).
An agent capable of preventing thrombotic, embolic and/or hemorrhagic disorders would be highly beneficial in patients who have high risk of thrombotic, embolic and/or hemorrhagic disorders.
Levosimendan, which is the (−)-enantiomer of [[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]hydrazono]propanedinitrile, and the method for its preparation is described in EP 565546 B1. Levosimendan is potent in the treatment of heart failure. Levosimendan increases contractility of the heart by increasing calcium sensitivity of contractile proteins in the cardiac muscle. Levosimendan is represented by the formula:

The hemodynamic effects of levosimendan in man are described in Sundberg, S. et al., Am. J. Cardiol., 1995; 75: 1061-1066 and in Lilleberg, J. et al., J. Cardiovasc. Pharmacol., 26(Suppl. 1), S63-S69, 1995. Pharmacokinetics of levosimendan in man after i.v. and oral dosing is described in Sandell, E.-P. et al., J. Cardiovasc. Pharmacol., 26(Suppl. 1), S57-S62, 1995. Clinical studies have confirmed the beneficial effects of levosimendan in heart failure patients.
Recently it has been found that levosimendan has an active metabolite (R)—N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamide (II) which is present in man following administration of levosimendan. The effects of (II) are similar to levosimendan. The use of (II) for increasing calcium sensitivity of contractile proteins in the cardiac muscle has been described in WO 99/66932.
Administration of levosimendan together with a thrombolytic agent in the treatment of acute myocardial infarction has been described in WO 03/063870. However, it has not been described that levosimendan would have antithrombotic effect or that levosimendan would reduce the risk of thrombotic, embolic and/or hemorrhagic disorders.